Field of the Invention
The present invention pertains to heat transfer compositions. More particularly the invention relates to automobile refrigerants comprising a hydrofluoroalkene, an iodocarbon, and at least one lubricant having hydrogen atoms and carbon atoms, wherein no more than 17% of the total number of hydrogen atoms which are attached to a carbon atom are tertiary hydrogen atoms.
Description of the Related Art
Compositions containing iodocarbon compounds have been disclosed as being particularly useful as heat transfer fluids. For example, international application PCT/US05/46982, filed Dec. 21, 2005, which is incorporated herein by reference, discloses compositions containing one or more fluoroolefins and the iodocarbon trifluoroiodomethane (CF3I) for use as refrigerants in applications such as automotive air conditioning systems. One advantage of compositions comprising iodinated compounds, and in particular compositions comprising trifluoroiodomethane, is that such compositions may be used as replacements for various other chlorinated and/or fluorinated compounds which have previously been used widely in refrigeration applications but which have tended to cause potential environmental damage as a result of such use. However, iodinated compounds, such as trifluoroiodomethane, tend to be relatively unstable, and often significantly less stable than certain CFCs, HCFCs and HFCs, especially under conditions that tend to occur in heat transfer systems in general and in refrigeration/air conditioning systems in particular. Although compositions containing iodocarbons, and in particular CF3I, can have substantial advantages when used in heat transfer applications, the use of such compositions presents heretofore unencountered and/or unrecognized problems. By way of example, compositions comprising iodocarbons, particularly compositions which comprise fluorinated olefins and iodocarbons, are frequently involved in a relatively complex chemical system under conditions of use, particularly as heat transfer fluids, that can cause unexpected results. In many typical heat transfer systems, such as automotive air conditioning systems, the refrigerant which comprises iodocarbon, such as CF3I, results in such a compound being exposed to certain of the metallic components of the refrigeration system at temperatures and under other conditions which promote the formation of iodine, iodide ions, organic radicals, and iodine containing inorganic acids.
It has been proposed to utilize certain iodocarbon compounds in refrigeration applications as replacements for certain of the CFCs and HCFCs that have heretofore been used. For example, Japanese Kokai 09-059612 (Application No. 07-220964) discloses refrigerant compositions comprising trifluoroiodomethane and one or more phenolic compounds. This document indicates that the phenolic compounds act to stabilize the trifluoroiodomethane against degradation. While compositions containing stabilizers for trifluoroiodomethane may enjoy a certain degree of success the use of a stabilizing agent alone may leave several embodiments of such compositions practically ineffective for use in commercially acceptable heat transfer systems. Furthermore, the stabilizing agent can contribute to unwanted and/or undesirable reactions in heat transfer systems. Applicants have come to appreciate that the use of refrigerants containing iodocarbons in accordance with conventional techniques, and even the prior techniques described by some of the present inventors in the patent application indicated above, leaves the need in many embodiments for yet further improvements in the refrigerant compositions and/or the refrigeration system.
Applicants have surprisingly found that the present compositions are capable of achieving continued high levels of performance such as refrigeration capacity and low levels of ozone depletion and global warming. The inventive compositions minimize the decomposition of the refrigerant system by selecting a lubricant having a reduced amount of tertiary hydrogen atoms. Therefore, one aspect of the present invention involves compositions which are suitable for use as heat transfer compositions which comprise a hydrofluoroalkene, an iodocarbon, and at least one lubricant having hydrogen atoms and carbon atoms, wherein no more than 17% of the total number of hydrogen atoms which are attached to a carbon atom are tertiary hydrogen atoms.